1. Field of the Invention
The present invention relates to a camera having sensors to detect various operations of the camera and multiple modes of operation and, more particularly, a camera with sensors to detect travel of the shutter and latching of the back cover of the camera, used in test and normal modes of operation of the camera.
2. Description of the Related Art
In cameras heretofore, the light rays from an subject were restricted by a stop in the lens, and furthermore the exposure time of the film was limited by a mechanical shutter. The shutter used in a single lens reflex camera fundamentally comprises two blinds, a front blind and a rear blind; before the exposure, the front blind covers the film image plane. By depressing the shutter button, firstly the front blind moves away from the image plane, and exposure of the film image plane commences. After a predetermined time has elapsed, the rear blind moves so as to cover the film image plane. The travel of the front blind and the rear blind is mechanically urged by spring force; the commencement of travel is effected by releasing the holding of the front blind and rear blind.
In the past, the control of these movements was purely mechanical, but in recent years electrical control has become widely used. Similarly to the past, spring force is used for the travel of the front blind and the rear blind, but the commencement of travel is controlled by the passage of current through electromagnets which hold the blinds.
On the other hand, increasing the speed of the shutter to 1/8,000 second and the like has become an important measure and, in addition, it has become necessary in recent years to increase the strobe synchronization speed to enable pictures to be taken in bright surroundings. For this object, it is necessary to make the travel speed of the front blind and rear blind (termed "blind speed" below) fast and in rapid succession by increasing the aforementioned spring force, and also to control to a narrow width the slit which is formed by the front blind and the rear blind.
In the case of high speed exposure times of 1/8,000 second, even if the current flow of the electromagnets is controlled with accurate timing, there is a possibility that the desired timing of the respective blinds will not be obtained. This is due to the speed of separation of the holding mechanisms controlled by the electromagnets and the variability of mechanical travel systems in which springs are included. Furthermore, because this kind of phenomenon can only become apparent after the film has been developed, a camera has been proposed having a shutter monitor which can test the exposure time.
The problems of accurate timing of the shutter become greatest when the highest speeds are used. However, there are few opportunities to use high speeds shorter than 1/8,000 second in normal photography. As a result, timing data were not easily obtained. In addition, not only a test of the shutter time, but also correction of the shutter time due to temperature changes and the like are desired.
Furthermore, in a camera having a shutter measurement device as proposed, there is a problem when the shutter is actuated with the back cover opened. Movement of the shutter vanes may be affected by the wind, etc., and be bent and strike the baseplate or cover plate.
In this kind of camera, when the camera is not used for a long period of time, for example, several days to several months, the first shutter action after this period of non-use is often unstable and the shutter time fluctuates. Accordingly, when a camera has been laid aside for a long period of time, there may be a large deviation in high speed operation in which the exposure time is short. In some instances, the front blind or the rear blind may not even open. In this case, because no test data on the shutter time is obtained, not only can characteristic phenomena not be found in the first shutter activation after a period of non-use, but also the shutter may be determined to be inoperative and the problem thought to be uncorrectable.